Rotary anode for an x-ray tube

ABSTRACT

A rotary anode of an X-ray tube delivers X-rays from at least the surface struck by electrons and consisting mostly of molybdenum. According to the present invention at least the struck location consists of substantially 75 percent molybdenum and up to 25 percent of a metal having an atomic number of 39 to 46.

Unite States Patent [191 Friedel et a1.

[ Sept. 17, 1974 ROTARY ANODE FOR AN X-RAY TUBE [75] Inventors: Rudolf Friedel, Erlangen, Germany;

Bernd Natter, Reutte, Austria [73] Assignee: Siemens Aktiengesellschaft,

Munich, Germany [22] Filed: June 12, 1973 [21] Appl. No.: 369,395

[30] Foreign Application Priority Data June 28, 1972 Germany 2231687 [52] US. Cl 313/330, 313/55, 313/311 [51] Int. Cl. H01j 35/08 [58] Field of Search 313/311, 330, 55, 60, 326

[56] References Cited UNITED STATES PATENTS I Sedlatschek et a1. 313/330- 3,737,699 6/1973 Gager 313/330 Primary Examiner-James W. Lawrence Assistant Examiner-Saxfield Chatmon, Jr. Attorney, Agent, or FirmRichards & Geier [5 7 ABSTRACT A rotary anode of an X-ray tube delivers X-rays from at least the surface struck by electrons and consisting mostly of molybdenum. According to the present invention at least the struck location consists of substantially 75 percent molybdenum and up to 25 percent of a metal having an atomic number of 39 to 46.

3 Claims, 2 Drawing Figures ROTARY ANODE FOR AN X-RAY TUBE This invention relates to a rotary anode of an X-ray tube which delivers X-rays from at least the surface struck by electrons and consisting mostly of molybdenum.

Such anodes are used primarily in soft ray diagnosis, for example, in examination of female breasts.

It is known to use for X-ray tubes anodes having surfaces which are struck by electrons and thus excited for the sending of X-rays, which are made of molybdenumor a molybdenum alloy, so as to produce rays of a wave length preferred for a specific purpose.

A drawback is that anodes made of molybdenum or molybdenum alloys have a quick drop in ray delivery. This drop shows outwardly on the anodes in the form of a roughened surface.

An object of the present invention is to prevent at least to a great extent, theabove-mentioned drop in ray delivery and its cause, namely, the roughening.

The present invention pertains to a rotary anode of an X-ray tube which produces X-ray tubes at locations struck by electrons and consisting primarily of molybdenum. In the accomplishment of the objectives of the present invention it was found desirable to make at least the struck surface of substantially 75 percent of molybdenum and up to 25 percent of a metal having the atomic number of 39 to 46. Alloys of this type have less inclination to crack formation since they have smaller inclination to thermal fatigue. The stated additions have a decisive advantage for the special use in female breast examination, in that their atomic number is close to that of molybdenum. Thus they do not produce a large proportion of hard rays which are detrimental for the exposure contrast.

According to an embodiment of the present invention the rotary anode of an X-ray tube consists of a plate of molybdenum or another material resistant to high temperatures which is mm thick. The plate is coated with a layer having a thickness of 1 mm and consisting of an alloy of 75 percent molybdenum and 25 percent niobium. Due to this arrangement the roughness as compared to pure molybdenum is greatly diminished and the characteristic ray composition of a Mo-anode is preserved to a great extent. Molybdenum becomes substantially more ductile even with 3 percent niobium in the alloy, so that there is a diminished roughness during ray production. Other mentioned metals have the same effect as long as they have a melting point which is above 1,500 C.

The invention will appear more clearly from the following detailed description when taken in connection with the accompanying drawing showing by way of example only, preferred embodiments of the inventive idea.

In the drawing:

FIG. 1 is side view, partly in section, of an entire X+ray tube provided with a rotary anode carrying a molybdenum alloy at the focal point path.

FIG. 2 is a section through a rotary anode for use with the tube shown in FIG. 1.

FIG. 1 shows an X-ray tube 2 with a container I having at one end the cathode arrangement 3 and at the other opposite end the anode arrangement 4. The cathode device is fixed by a sleeve 5 to one end of the container] and has a shoulder 6 carrying the actual glow cathode 14. Opposite the cathode device at the other end of tube container 1 is the anode device carrying a rotor 7 for driving the rotary anode 9 connected with it by an axle 8. The rotary anode itself consists of a plate 10 which is I0 mm thick and consists of molybdenum'and 5 percent tungsten. The plate is pressed by a screw 11 against the counter bearing 12 of the'axle 8 and is rotatable by the rotor 7 and a stator (not shown). Upon its outer surface directed toward the cathode device 3 the plate 10 carries upon its edge a coating 13 having a thickness of I mm andconsisting of an alloy containing 97 percent molybdenum and 3 percent niobium.

When a corresponding voltage is provided between the lines 15, l6'and 17 and the support 18, electrons are produced by the glow cathode 14 which strike this coating and release X-rays in the focal point paths l9 and 20, individually or jointly depending upon the manner in which the cathode is operated, the X-rays being used in X-ray technology.

What is claimed is:

l. A rotary anode for an X-ray tube, having a surface to be struck by electrons for producing X-rays, said surface consisting of an alloy having up to 25 percent of niobium and at least percent of molybdenum.

2. A rotary anode according to claim 1, comprising a body consisting of a refractory material and having a coating consisting of said alloy.

3. A rotary anode according to claim 2, wherein said refractory material is molybdenum. 

2. A rotary anode according to claim 1, comprising a body consisting of a refractory material and having a coating consisting of said alloy.
 3. A rotary anode according to claim 2, wherein said refractory material is molybdenum. 